An early concept for the 747 advanced (which eventually became the -8) was for inboard GE90s and outboard CF6-80C2s
. Fortunately that died.
Would a twin engine 747 be feasible without a complete redesign?
Since engine thrust is based on "engine out" requirements, it would take a ~200,000 lb thrust class engine if you want to retain the same MTOW as the 747-8..
HH, Boeing is supposedly at the point this year where it's costing less to build a 787 than they're selling them for (finally - only line number 450 to get there
). So it's at least looking like the 787 won't be a big money pit.
Airbus is into the A380 something like 20 billion, and while they are finally to the point where they're getting positive cash flow on new production, that's not going to last as they're dropping production down to 1/month. When Airbus launched the A380, they predicted a market for 1,200 VLA between 2007 and 2027. Half way there, barely 300 total A380s and 747-8s have been delivered, with total outstanding orders for ~150 more (many of which are soft).
Is spending another ~5 billion on a A380 neo - so far with only one interested customer - a good business decision or good money after bad?
